Classifying failure reports as either current or stale for mobility robustness optimization adjustments

ABSTRACT

The present disclosure relates to identifying stale failure reports in a cellular communications network. In one embodiment, a node in a cellular communications network receives a failure report associated with a connection failure for a user equipment and determines when the connection failure occurred with respect to a most recent mobility adjustment made by the node. If the connection failure occurred before the most recent mobility adjustment made by the node, the node classifies the failure report as a stale failure report. In one embodiment, if the failure report is classified as a stale failure report, the node discards the failure. In another embodiment, if the failure report is classified as a stale failure report, the node considers the failure report with reduced relevance for a next iteration of a process to determine whether new mobility adjustments are desired.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/888,778, filed May 7, 2013, now U.S. Pat. No. ______, which claimsthe benefit of provisional patent application Ser. No. 61/645,868, filedMay 11, 2012, the disclosures of which are hereby incorporated herein byreference in their entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to reporting connection failures in acellular communications network.

BACKGROUND

One issue that must be handled by all cellular communications networksis mobility of mobile devices. In particular, a cellular communicationsnetwork must enable handovers of mobile devices between cells within thesame Radio Access Network (RAN) as well as enable handover of mobileterminals between different RANs. A common mobility issue is mobilityconnection failures, i.e., connection failures during or shortly afterthe handover process. In order to address this mobility issue, accordingto discussions in the 3^(rd) Generation Partnership Project (3GPP), amobile device, which is referred to as a User Equipment or User Element(UE), is required to transmit a failure report to the cellularcommunications network whenever a mobility connection failure occurs.The failure report will then be used by a Mobility RobustnessOptimization (MRO) function of the cellular communications network tooptimize mobility settings, or mobility parameters, that controlhandovers within the cellular communications network.

With respect to Inter-Radio Access Technology (IRAT) handovers (HOs),3GPP RAN Working Group 3 (WG3) has identified multiple high priorityscenarios that present mobility issues and therefore need to beaddressed. As illustrated in FIGS. 1A and 1B, an IRAT HO is a handoverof a UE 10 between a cell 12 served by a base station (BS) 14 in a RANoperating according to one Radio Access Technology (RAT) (e.g., anenhanced Node B (eNB) in a RAN of a 4G Long Term Evolution (LTE)cellular communications network) and a cell 16 served by a base station18 in another RAN operating according to another RAT (e.g., a Node B ina Universal Terrestrial Radio Access Network (UTRAN) of a 3G UniversalMobile Telecommunications System (UMTS) cellular communicationsnetwork). In particular, the scenarios identified by 3GPP RAN WG3 are:

-   -   Scenario 1: A mobility connection failure, specifically a Radio        Link Failure (RLF), while in an LTE RAN or during a HO from the        LTE RAN to a 2G/3G RAN (e.g., a UTRAN) followed by a        reconnection to the 2G/3G RAN (i.e., a too late HO from an LTE        RAN to a 2G/3G RAN).    -   Scenario 2: A mobility failure during or after a HO from a 2G/3G        RAN (e.g., a UTRAN) to an LTE RAN followed by a reconnection        back to the 2G/3G RAN (i.e., the source RAT). The reconnection        may be to the source cell for the HO or a different cell in the        2G/3G RAN. This is referred to herein as a too early HO from a        2G/3G RAN to an LTE RAN.        -   Scenario 2a: A handover failure (HOF) during the HO from the            2G/3G RAN to the LTE RAN (i.e., a HOF during a Random Access            Channel (RACH) attempt in the LTE RAN) followed by the            reconnection back to the 2G/3G RAN.        -   Scenario 2b: An RLF in the LTE RAN shortly after the HO from            the 2G/3G RAN to the LTE RAN (i.e., an RLF after successful            RACH in the LTE RAN) followed by the reconnection back to            the 2G/3G RAN.

Triggering of an IRAT HO from a cell in an LTE RAN to a cell in a UTRANis controlled by mobility parameters in the LTE RAN associated with bothReference Signal Received Power (RSRP) and Reference Signal ReceivedQuality (RSRQ) measurement types. These mobility parameters in the LTERAN form a HO threshold, which is referred to herein as ho_thresh_lte.One way to optimize Scenario 1 (i.e., too late HOs from LTE RAN to 2G/3GRAN, e.g., a UTRAN) is to increase the value of ho_thresh_lte in orderto trigger HOs from the LTE RAN to the 2G/3G RAN earlier. However, doingso may increase the number of unnecessary HOs, i.e., HOs from the LTERAN to the 2G/3G RAN even when the coverage of the LTE RAN is sufficientto maintain the connection. This tradeoff between decreasing the numberof too late HOs and increasing the number of unnecessary HOs isillustrated in FIG. 2. An MRO algorithm should take this tradeoff intoaccount to increase or decrease ho_thresh_lte.

Triggering of an IRAT HO from a cell in a UTRAN to a cell in an LTE RANis controlled by other mobility parameters in the UTRAN associated withboth RSRP and RSRQ measurement types. These mobility parameters in theUTRAN form a HO threshold, which is referred to herein asho_thresh_utran. One way to optimize Scenario 2 (i.e., too early HOsfrom 2G/3G RAN, e.g., a UTRAN or Global System for Mobile Communications(GSM) Enhanced Data Rates for Global Evolution (EDGE) RAN (GERAN), to anLTE RAN) is to increase the value of ho_thresh_utran in order to onlytrigger a HO to the LTE RAN when the signal from the LTE RAN is strongenough to retain the connection. However, doing so may unnecessarilyincrease time in the UTRAN if ho_thresh_utran is set too high such thatthe UE 10 remains in the UTRAN even when the coverage of the LTE RAN issufficient to retain a connection with the UE 10. This tradeoff isillustrated in FIG. 3 and should be taken into account by an MROalgorithm when increasing or decreasing the ho_thresh_utran.

The occurrence of too late and unnecessary HOs from an LTE RAN to a2G/3G RAN are to be detected via RLF reports and unnecessary HOindicators. Procedures to be performed upon RLF detection arestandardized in 3GPP Technical Specification (TS) 36.311 section5.3.11.3. At the UE 10, when an RLF is detected, various information isstored in an RLF report as illustrated in FIG. 4. In the case where theRLF is followed by a Radio Resource Control (RRC) connectionre-establishment procedure, the UE 10 sets the reestablishmentCellId inthe RLF report to a global cell identity of the selected cell.Additional information to be reported in support of the MRO functionparticularly with respect to IRAT HOs is currently under discussion in3GPP RAN3. At this point, the discussions are initially progressingtowards a decision about how to make the RLF reports available to thedifferent RATs as explained below.

Different solutions to making RLF reports associated with IRAT HOsavailable to the different RATs running MRO algorithms have beenproposed. These solutions are described in 3GPP Written ContributionR3-120390, which is entitled “IRAT MRO way forward” and was presented in3GPP Meeting R3-75 which was held from Feb. 6, 2012 through Feb. 10,2012 in Dresden, Germany. As described in 3GPP Written ContributionR3-120390 and discussed below, there are four different solutions.

Solution 1: The first solution is reporting the RLF when returning tothe LTE RAN. More specifically, for both Scenario 1 and Scenario 2discussed above, when the UE reconnects to the 2G/3G RAN after themobility failure, the UE stores the necessary information for thecorresponding failure report. Then, when the UE is back in the LTE RAN,the failure information is transmitted to the LTE RAN as, for example,an RLF report. The base station in the LTE RAN that obtains the RLFreport from the UE forwards the RLF to the base station that serves thecell where the corresponding mobility connection failure occurred viaappropriate signaling (e.g., X2 or S1 signaling for Scenarios 1 and 2band RAN Information Message (RIM) to the Radio Network Controller (RNC)of the base station serving the cell in the 2G/3G RAN before the IRAT HOfor Scenario 2a).

Solution 1 for Scenario 1 is illustrated in FIG. 5. As illustrated, a UEexperiences an RLF in the LTE RAN. After the RLF, the UE connects toCell Y in the 3G RAN and stores the RLF report. Subsequently, when theUE reconnects to the LTE RAN by, in this example, an IRAT HO from Cell Yin the 3G RAN to Cell B in the LTE RAN, the UE sends the RLF report tothe base station corresponding to Cell B in the LTE RAN. The basestation corresponding to Cell B sends the RLF report to the base stationcorresponding to Cell A where the RLF occurred. The MRO function of thebase station for Cell A determines that an amount of time that the UEwas connected to Cell A before the RLF (Δt) is greater than a predefinedminimum amount of time (t_min) and, as such, the RLF was due to a toolate IRAT HO from the LTE RAN to the 3G RAN.

Solution 1 for Scenario 2a is illustrated in FIG. 6. After a HO failure(i.e., unsuccessful RACH attempts) during an IRAT HO from Cell X of the3G RAN to Cell A of the LTE RAN, the UE reconnects to Cell Y of the 3GRAN. Subsequently, when the UE reconnects to the LTE RAN by, in thisexample, an IRAT HO from Cell Y in the 3G RAN to Cell B in the LTE RAN,the UE sends the RLF report to the base station corresponding to Cell Bin the LTE RAN. The base station corresponding to Cell B in the LTE RANdetermines that the mobility failure is an IRAT HOF from Cell X in the3G RAN and, as such, sends the RLF report to the RNC for the basestation corresponding to Cell X of the 3G RAN via a RIM.

Solution 1 for Scenario 2b is illustrated in FIG. 7. Shortly after anIRAT HO from Cell X of the 3G RAN to Cell A of the LTE RAN, the UEexperiences an RLF. After the RLF, the UE reconnects to Cell Y of the 3GRAN. Subsequently, when the UE reconnects to the LTE RAN by, in thisexample, an IRAT HO from Cell Y in the 3G RAN to Cell B in the LTE RAN,the UE sends the RLF report to the base station corresponding to Cell Bin the LTE RAN. The base station corresponding to Cell B in the LTE RANdetermines that the mobility failure is an RLF shortly after the IRAT HOfrom Cell X in the 3G RAN to Cell A in the LTE RAN (i.e., the IRAT is atoo early IRAT) and, as such, sends the RLF report to the RNC for thebase station corresponding to Cell X of the 3G RAN via a RIM. Inaddition, the base station corresponding to Cell B may send the RLFreport to the base station corresponding to Cell A in the LTE RAN wherethe RLF occurred via suitable signaling (e.g., X2 or S1).

Solution 2: The second solution is reporting the failure to the 2G/3GRAN and/or the LTE RAN where the UE reconnects after the mobilityfailure. More specifically, Solution 2 for Scenario 1 is illustrated inFIG. 8. As illustrated, the UE experiences an RLF in Cell A of the LTERAN due to a too late HO to the 3G RAN. After the RLF, the UE stores theRLF report and sends the RLF report to the 3G RAN upon reconnecting toCell Y of the 3G RAN. The RNC of the base station corresponding to CellY of the 3G RAN determines that the RLF report is the result of a toolate IRAT HO from Cell A of the LTE RAN and therefore sends the RLFreport to the base station corresponding to Cell A of the LTE RAN via aRIM.

Solution 2 for Scenario 2a is illustrated in FIG. 9. As illustrated,after a HO failure (i.e., unsuccessful RACH attempts) during an IRAT HOfrom Cell X of the 3G RAN to Cell A of the LTE RAN, the UE stores acorresponding RLF report and sends the RLF report to the 3G RAN uponreconnecting to Cell Y of the 3G RAN. The RNC of the base stationcorresponding to Cell Y of the 3G RAN determines that the RLF report isthe result of a too early IRAT HO from Cell X of the 3G RAN to Cell A ofthe LTE RAN. In addition, the RNC may send the RLF report to the basestation corresponding to Cell A of the LTE RAN via a RIM. Notably, theRLF report can be used by the MRO function of the RNC and/or an MROfunction of the base station corresponding to Cell A of the LTE RAN. Ifthe UE reconnects to the LTE RAN after the failure and the RLF report isnot yet reported to the LTE RAN, the UE may send the RLF report to aserving base station in the LTE RAN. The serving base station can thenforward the RLF report to the RNC of the base station corresponding toCell X in the 3G RAN via a RIM and, if desired, send the RLF report tothe base station corresponding to Cell A in the LTE RAN.

Solution 2 for Scenario 2b is illustrated in FIG. 10. As illustrated,shortly after an IRAT HO from Cell X of the 3G RAN to Cell A of the LTERAN, the UE experiences an RLF. After the RLF, the UE stores an RLFreport and sends the RLF report to the 3G RAN upon reconnecting to CellY of the 3G RAN. The RNC of the base station corresponding to Cell Y ofthe 3G RAN determines that the RLF report is the result of a too earlyIRAT HO from Cell X of the 3G RAN to Cell A of the LTE RAN. In addition,the RNC may send the RLF report to the base station corresponding toCell A of the LTE RAN via a RIM. Notably, the RLF report can be used bythe MRO function of the RNC and/or an MRO function of the base stationcorresponding to Cell A of the LTE RAN. If the UE reconnects to the LTERAN after the failure and the RLF report is not yet reported to the LTERAN, the UE may send the RLF report to a serving base station in the LTERAN. The serving base station can then forward the RLF report to the RNCof the base station corresponding to Cell X in the 3G RAN via a RIM and,if desired, send the RLF report to the base station corresponding toCell A in the LTE RAN.

Solution 3: The third solution is reporting the RLF to the RAT where thefailure occurred and reporting the HO failure in the RAT of the cell inwhich the HO command was received. More specifically, Solution 3 forScenario 1 is illustrated in FIG. 11. Notably, Solution 3 for Scenario 1is the same as Solution 1 for Scenario 1. As illustrated, a UEexperiences an RLF in the LTE RAN. After the RLF, the UE connects toCell Y in the 3G RAN and stores the RLF report. Subsequently, when theUE reconnects to the LTE RAN by, in this example, an IRAT HO from CellYin the 3G RAN to Cell B in the LTE RAN, the UE sends the RLF report tothe base station corresponding to Cell B in the LTE RAN. The basestation corresponding to Cell B sends the RLF report to the base stationcorresponding to Cell A where the RLF occurred. The MRO function of thebase station for Cell A determines that an amount of time that the UEwas connected to Cell A before the RLF (Δt) is greater than a predefinedminimum amount of time (t_min) and, as such, the RLF was due to a toolate IRAT HO from the LTE RAN to the 3G RAN.

Solution 3 for Scenario 2a is illustrated in FIG. 12. As illustrated,after a HO failure (i.e., unsuccessful RACH attempts) during an IRAT HOfrom Cell X of the 3G RAN to Cell A of the LTE RAN, the UE stores acorresponding RLF report and sends the RLF report to the 3G RAN uponreconnecting to Cell Y of the 3G RAN. The RNC of the base stationcorresponding to Cell Y of the 3G RAN determines that the RLF report isthe result of a too early IRAT HO from Cell X of the 3G RAN to Cell A ofthe LTE RAN. If desired, the RNC sends the RLF report to the basestation corresponding to Cell A of the LTE RAN via a RIM.

Solution 3 for Scenario 2b is illustrated in FIG. 13. Notably, Solution3 for Scenario 2b is the same as Solution 1 for Scenario 2b. Shortlyafter an IRAT HO from Cell X of the 3G RAN to Cell A of the LTE RAN, theUE experiences an RLF. After the RLF, the UE reconnects to Cell Y of the3G RAN. Subsequently, when the UE reconnects to the LTE RAN by, in thisexample, an IRAT HO from Cell Y in the 3G RAN to Cell B in the LTE RAN,the UE sends the RLF report to the base station corresponding to Cell Bin the LTE RAN. The base station corresponding to Cell B in the LTE RANdetermines that the mobility failure is an RLF shortly after the IRAT HOfrom Cell X in the 3G RAN to Cell A in the LTE RAN (i.e., the IRAT is atoo early IRAT) and, as such, sends the RLF report to the RNC for thebase station corresponding to Cell X of the 3G RAN via a RIM. Inaddition, the base station corresponding to Cell B may send the RLFreport to the base station corresponding to Cell A in the LTE RAN wherethe RLF occurred via suitable signaling (e.g., X2 or S1).

Solution 4: The fourth solution is sending the RLF report when returningto the LTE RAN in the case of a too late IRAT HO from the LTE RAN to the2G/3G RAN and detecting the connection failure at the RNC of the 2G/3GRAN in the case of a too early IRAT HO from the 2G/3G RAN to the LTERAN. Solution 4 for Scenario 1 is illustrated in FIG. 14 and is the sameas that for Solution 1, Scenario 1. For Solution 4, Scenarios 2a and 2b,the UE does not report the connection failure to the network. Rather,the RNC of the 2G/3G network can understand that the UE was previouslycamped on the 2G/3G network and is returning to the 2G/3G network aftera connection failure during an IRAT HO to the LTE RAN.

As discussed in the Detailed Description below in detail, the inventorshave found that the solutions for obtaining the RLF reports from the UEsin the various scenarios discussed above give rise to new issues withrespect to delayed RLF reporting. As such, there is a need for systemsand methods that address these new issues.

SUMMARY

The present disclosure relates to identifying stale failure reports in acellular communications network. In one embodiment, a node in a cellularcommunications network receives a failure report associated with aconnection failure for a User Equipment (UE) and determines when theconnection failure occurred with respect to a most recent mobilityadjustment made by the node. If the connection failure occurred beforethe most recent mobility adjustment made by the node, the nodeclassifies the failure report as a stale failure report. In oneembodiment, if the failure report is classified as a stale failurereport, the node discards the failure report such that the failurereport is not considered for a next iteration of a process to determinewhether new mobility adjustments are desired. In another embodiment, ifthe failure report is classified as a stale failure report, the nodeconsiders the failure report with reduced relevance for a next iterationof a process to determine whether new mobility adjustments are desired.

In one embodiment, the failure report includes timing data that isindicative of a time at which the connection failure occurred, and thenode determines when the connection failure occurred with respect to themost recent mobility adjustment made by the node based on the timingdata. In one particular embodiment, the timing data includes a firsttimer value that defines an amount of time that has expired between thetime at which the connection failure occurred and a time at which the UEtransmitted the failure report, and the node determines when theconnection failure occurred with respect to the most recent mobilityadjustment made by the node based on the first timer value and a secondtimer value that defines an amount of time that has expired since themost recent mobility adjustment was made by the node.

In one embodiment, if the connection failure occurred after the mostrecent mobility adjustment made by the node, the node classifies thefailure report as a current failure report. In one embodiment, if thefailure report is classified as a current failure report, the nodeconsiders the failure report for a next iteration of a mobilityoptimization process.

In one embodiment, a UE in a multiple Radio Access Technology (RAT)cellular communications system detects a connection failure andthereafter transmits a failure report, where the failure report isassociated with the connection failure and includes timing data that isindicative of a time at which the connection failure occurred. In oneembodiment, the timing data includes a timer value that defines anamount of time that has expired between a time at which the connectionfailure occurred and a time at which the UE transmitted the failurereport to the cellular communications network. In one particularembodiment, the UE starts the timer in response to detecting theconnection failure. Thereafter, the UE detects a triggering event fortransmitting the failure report and, in response to the triggeringevent, stops the timer and transmits the failure report including avalue of the timer to the cellular communications network.

In one embodiment, the connection failure is a radio link failure in acell served by a first base station in a first radio access networkoperating according to a first radio access technology, and the UEtransmits the failure report to a base station in the first radio accessnetwork after reconnecting to the first radio access network. In oneparticular embodiment, the connection failure is a radio link failure ina cell served by a first base station in a first radio access networkoperating according to a first radio access technology, and the UEinitially reconnects to a base station in a second radio access networkoperating according to a second radio access technology after the radiolink failure. Sometime after reconnecting to the base station in thesecond radio access network, the UE connects to a base station in thefirst radio access network to thereby reconnect to the first radioaccess network, and the UE transmits the failure report to the basestation in the first radio access network after reconnecting to thefirst radio access network.

In one embodiment, the connection failure is a connection failureassociated with a handover from a cell served by a first base station ina first radio access network operating according to a first radio accesstechnology to a cell served by a second base station in a second radioaccess network operating according to a second radio access technology.In this embodiment, the UE transmits the failure report to a basestation in the second radio access network operating according to thesecond radio access technology after subsequently connecting to the basestation in the second radio access network.

In one particular embodiment, the connection failure is a connectionfailure associated with a handover from a cell served by a first basestation in a first radio access network operating according to a firstradio access technology to a cell served by a second base station in asecond radio access network operating according to a second radio accesstechnology. In this embodiment, the UE initially connects to a basestation in the first radio access network after the connection failure.Sometime thereafter, the UE connects to a base station in the secondradio access network and transmits the failure report to the basestation in the second radio access network after connecting to the basestation in the second radio access network.

In one embodiment, the connection failure is a radio link failure in acell served by a first base station in a first radio access networkoperating according to a first radio access technology, and the UEtransmits the failure report to a second base station in a second radioaccess network operating according to a second radio access technologyafter connecting to the second base station of the second radio accessnetwork. In one particular embodiment, the connection failure is a radiolink failure in a cell served by a first base station in a first radioaccess network operating according to a first radio access technology.Further, after the radio link failure, the UE connects to a second basestation in a second radio access network operating according to a secondradio access technology and transmits the failure report to the secondbase station in the second radio access network after connecting to thesecond base station of the second radio access network.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description of the preferred embodiments inassociation with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the disclosure, andtogether with the description serve to explain the principles of thedisclosure.

FIGS. 1A and 1B illustrate Inter-Radio Access Technology (IRAT)handovers (HOs) in a cellular communications network according to oneembodiment of the present disclosure;

FIG. 2 illustrates a tradeoff between decreasing the number of RadioLink Failures (RLFs) due to too late IRAT HOs from a Long Term Evolution(LTE) Radio Access Network (RAN) to a Universal Terrestrial Radio AccessNetwork (UTRAN) and increasing the number of unnecessary IRAT HOs fromthe LTE RAN to the UTRAN when increasing a corresponding IRAT HOthreshold;

FIG. 3 illustrates a tradeoff between decreasing the number of HOFailures (HOFs) due to too early IRAT HOs from a UTRAN to an LTE RAN andunnecessarily increasing time in the UTRAN when increasing acorresponding IRAT HO threshold;

FIG. 4 illustrates information stored in an RLF report according to thepresent version of 3^(rd) Generation Partnership Project TechnicalSpecification (3GPP TS) 36.331;

FIGS. 5 through 14 graphically illustrate four different solutions forsending failure reports to the cellular communications network fordifferent scenarios of connection failures associated with IRAT HOs;

FIG. 15 illustrates late reporting of a connection failure to a node ina cellular communications network performing a Mobility RobustnessOptimization (MRO) function, which can occur in many of the solutionsand scenarios illustrated in FIGS. 5 through 14;

FIG. 16 is a flow chart that illustrates a process for classifying afailure report received by a node that performs an MRO function aseither current or stale according to one embodiment of the presentdisclosure;

FIG. 17 is a flow chart that illustrates the operation of a UserEquipment or User Element (UE) to send, or transmit, a failure report toa cellular communications network, where the failure report includestiming data that is indicative of a time at which an associatedconnection failure occurred according to one embodiment of the presentdisclosure;

FIG. 18 is a flow chart that illustrates the operation of a node in acellular communications network that performs an MRO function to receiveand classify failure reports based the timing data included in thefailure reports according to the process of FIG. 17 as well as timingdata that defines a time at which a most recent MRO adjustment was madeby the node according to one embodiment of the present disclosure;

FIG. 19 illustrates a cellular communications network that includes a 4GLTE cellular communications network and a 3G Universal Mobile TelephonySystem (UMTS) cellular communications network in which IRAT HOs occurbetween an LTE RAN of the 4G LTE cellular communications network and aUTRAN of the UMTS cellular communications network, wherein failurereports transmitted by UEs for connection failures include timing datathat is utilized by appropriate MRO functions to classify the failurereports as current or stale according to one embodiment of the presentdisclosure;

FIG. 20 through 29 illustrate transmission of failure reports for eachof the solutions and scenarios of FIGS. 5 through 14 in which thefailure reports including timing data that enable classification of thefailure reports as either current or stale according to variousembodiments of the present disclosure;

FIG. 30 is a block diagram of a UE according to one embodiment of thepresent disclosure;

FIG. 31 is a block diagram of a base station according to one embodimentof the present disclosure; and

FIG. 32 is a block diagram of a Radio Network Controller (RNC) accordingto one embodiment of the present disclosure.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the embodiments andillustrate the best mode of practicing the embodiments. Upon reading thefollowing description in light of the accompanying drawing figures,those skilled in the art will understand the concepts of the disclosureand will recognize applications of these concepts not particularlyaddressed herein. It should be understood that these concepts andapplications fall within the scope of the disclosure and theaccompanying claims.

As discussed in the Background, with respect to Inter-Radio AccessTechnology (IRAT) handovers (HOs) in a multiple Radio Access Technology(RAT) cellular communications system, 3^(rd) Generation PartnershipProject (3GPP) Radio Access Network (RAN) Working Group 3 (WG3) hasidentified multiple high priority scenarios that present mobility issuesand therefore need to be addressed. Again, the scenarios identified by3GPP RAN WG3 are:

-   -   Scenario 1: A mobility connection failure (also referred to        herein as simply a connection failure), specifically a Radio        Link Failure (RLF), while in a Long Term Evolution (LTE) RAN or        during a HO from the LTE RAN to a 2G/3G RAN (e.g., a Universal        Terrestrial Radio Access Network (UTRAN)) followed by a        reconnection to the 2G/3G RAN (i.e., a too late HO from an LTE        RAN to a 2G/3G RAN).    -   Scenario 2: A mobility failure during or after a HO from a 2G/3G        RAN (e.g., a UTRAN) to an LTE RAN followed by a reconnection        back to the 2G/3G RAN (i.e., the source RAT). The reconnection        may be to the source cell for the HO or a different cell in the        2G/3G RAN. This is referred to herein as a too early HO from a        2G/3G RAN to an LTE RAN.        -   Scenario 2a: A handover failure (HOF) during the HO from the            2G/3G RAN to the LTE RAN (i.e., a HOF during a Random Access            Channel (RACH) attempt in the LTE RAN) followed by the            reconnection back to the 2G/3G RAN.        -   Scenario 2b: An RLF in the LTE RAN shortly after the HO from            the 2G/3G RAN to the LTE RAN (i.e., an RLF after successful            RACH in the LTE RAN) followed by the reconnection back to            the 2G/3G RAN.            Further, for IRAT HOs between an LTE RAN and a 2G/3G RAN,            multiple solutions for making RLF reports associated with            IRAT HOs available to the different RATs running Mobility            Robustness Optimization (MRO) algorithms have been proposed.            As discussed in the Background, these solutions include:    -   Solution 1: Reporting the RLF when returning to the LTE RAN.    -   Solution 2: Reporting the failure to the 2G/3G RAN and/or the        LTE RAN where the UE reconnects after the mobility failure.    -   Solution 3: Reporting the RLF to the RAT where the failure        occurred and reporting the HO failure in the RAT of the cell in        which the HO command was received.    -   Solution 4: Reporting the RLF when returning to the LTE RAN in        the case of a too late IRAT HO from the LTE RAN to the 2G/3G RAN        and detecting the connection failure at the RNC of the 2G/3G RAN        in the case of a too early IRAT HO from the 2G/3G RAN to the LTE        RAN.

The inventors have found that, when using the solutions discussed abovefor making failure reports available to the cellular communicationsnetwork, one issue that arises is that there may be delays between atime at which a User Equipment or User Element (UE) experiences aconnection failure and a time at which the UE reports the connectionfailure. Delays in reporting the connection failure may be due to a longdelay before the UE reconnects to the RAN where the connection failureis to be reported (e.g., Solution 1), due to the UE transitioning to anidle mode for a long time before reconnecting to the RAN where theconnection failure is to be reported, or due to a failure of thecellular communications network to request reporting of the RLF reportfor a long time. Thus, an MRO function that performs MRO for a cell in,for example, an LTE RAN may perform an MRO process that results inadjustment(s) to mobility parameters (i.e., mobility adjustments) forthe cell based on failure reports received in a timely manner. However,due to the issue of delayed reporting, the MRO function may continue toreceive failure reports after the mobility adjustment(s) have been madewhere the failure reports are relevant to a time window prior to makingthe mobility adjustment(s). Using current MRO algorithms, these “stale”failure reports are still considered with the same relevance as timelyfailure reports for the next iteration of the MRO process. The stalefailure reports may lead to incorrect or undesirable mobilityadjustments and slow convergence of the cellular communications networkto a state of stable mobility.

As an example, FIG. 15 illustrates stale failure reports for Solution 1,Scenario 1 after RLFs due to too late HOs from an LTE RAN to a 3G RAN.For Solution 1, UEs do not report failures until they return to the LTERAN and, as a result, there is a delay if the UEs do not initiallyreconnect back to the LTE RAN after the RLF. This delay may be quitelong due to two reasons: (1) the HO from the 3G RAN to the LTE RAN maybe disabled by operators in order to avoid ping pongs between the LTERAN and the 3G RAN and (2) UEs reconnect to the LTE RAN via cellreselection, which is a UE controlled procedure (i.e., the UEs maydecide to stay camped in the 3G RAN if desired). It is very likely thatMRO functions running on the base stations in the LTE RAN and/or MROfunctions running on Radio Network Controllers (RNCs) in the 3G RAN willtrigger mobility adjustments periodically in response to some eventoccurrence and/or based on reception of a minimum number of reports,which can be RLF reports, unnecessary HO reports, or ping pong reports.

In this example, N=N1+N2 UEs have suffered too late HOs from Cell A ofthe LTE RAN to Cell X of the 3G RAN and all N of the UEs reconnected toCell Y of the 3G RAN after the corresponding RLFs in Cell A of the LTERAN due to the too late HOs. After some time, N1 of the UEs havereconnected to Cell B of the LTE RAN and transmitted corresponding RLFreports to a base station (eNB 1) corresponding to Cell B in the LTERAN. Assuming that eNB 1 serves both Cell A and Cell B of the LTE RAN,an MRO process of the eNB 1 is triggered at a certain time (t0) todetermine whether mobility adjustments, or MRO adjustments, are neededand, if so, make the mobility adjustments. After the time (t0), new UEsmay eventually suffer from too late or unnecessary HOs and, when thosenew UEs return to the LTE RAN, the new UEs send new RLF reports to beused for a next iteration of the MRO process.

After the time (t0), eNB1 will also receive RLF reports from the otherN2 UEs if those UEs send RLF reports to the LTE RAN within 48 hoursafter the failure according to 3GPP Technical Specification (TS) 36.331.In the current standard, there is no support for eNB 1 to recognize thatthe RLF reports from those N2 UEs are not associated with the currentmobility parameter settings in eNB 1. Therefore, it is not possible foreNB 1 to discard the RLF reports from the N2 UEs such that the RLFreports are not considered for the subsequent iteration of the MROprocess at eNB 1. As such, the RLF reports from the N2 UEs, which arereferred to herein as stale RLF reports, will impact the robustness ofthe MRO adjustments and the MRO convergence proportionally to N2/N.

In the other Solutions, i.e., Solutions 2, 3, and 4, RLF reports aremade available to other nodes which possibly run MRO algorithms. Inthese solutions, a stale RLF may occur, for example, if a UE goes toidle mode after the failure and returns to active mode after a long timeor if the network fails to request reporting of the RLF report for along time. The problem of stale RLF reports will also exist even if theRLF reports are available faster than in Solution 1. For example, it canbe assumed that a certain number of failures occur minutes before aniteration of the MRO process is performed and, even though correspondingRLF reports are available minutes later, the RLF reports are stale.

The present disclosure provides systems and methods that address stalereporting of connection failures in a cellular communication network.Stale failure reports can be discarded such that they are not consideredfor a subsequent iteration of a mobility optimization process (e.g., anMRO process) or considered for the subsequent iteration of the mobilityoptimization process but with reduced relevance. Notably, while many ofthe embodiments described below relate to classification of failurereports with respect to IRAT HOs, the concepts disclosed herein areequally applicable to failure reports for intra-RAT HOs (i.e., HOsbetween cells in the same RAT). Further, although many of theembodiments discussed below relate to classification of failure reportswith respect to IRAT HOs between a 4G LTE cellular communicationsnetwork and a 2G/3G cellular communications network, the conceptsdescribed herein are not limited to any particular RATs.

In this regard, FIG. 16 is a flow chart that illustrates a process forcharacterizing a failure report according to one embodiment of thepresent disclosure. In this embodiment, the process of FIG. 16 isperformed by a node in a cellular communications network that performs aprocess for adjusting, or updating, mobility parameters, which isreferred to herein as an MRO process. As used herein, a mobilityparameter is a parameter utilized to control mobility, or HOs, of awireless device, or UE, within a cellular communications network (e.g.,a Reference Signal Received Power (RSRP) or Reference Signal ReceivedQuality (RSRQ) threshold). More specifically, a mobility parameter is aparameter utilized to control HOs from one cell to a neighboring cell,where the two cells may be in the same RAN (i.e., for intra-RAT HOs) orin different RANs operating according to different RATs (i.e., for IRATHOs). Mobility parameters generally include mobility thresholds (e.g.,RSRP and/or RSRQ thresholds). A mobility adjustment is an adjustment ofone or more mobility parameters for a specific neighboring cell.Further, the mobility adjustment may affect mobility parameters such asmobility thresholds between different source and target entities. Forexample, the mobility adjustment may be applied between a source cell toa target cell or between a source cell to a target frequency or betweena source cell to a target RAT. The node that performs the process ofFIG. 16 can be, for example, a base station in the cellularcommunications network (e.g., an enhanced Node B (eNB) of an LTEcellular communications network), an RNC (e.g., an RNC of a base stationin a Universal Mobile Telecommunications System (UMTS) cellularcommunications network), or the like.

As illustrated, the node receives a failure report associated with aconnection failure for a UE (step 1000). As used herein, a failurereport is generally information that notifies or reports a connectionfailure experienced by the UE, where the connection failure is morespecifically a mobility connection failure. In one particularembodiment, the failure report is an RLF report. As discussed below, thefailure report includes timing data that is indicative of a time atwhich the connection failure occurred. In one preferred embodiment, thetiming data is or includes a timer value that defines an amount of timethat has expired between the time at which the connection failureoccurred and a time at which the UE reported the connection failure bytransmitting the failure report to an appropriate node. However, thetiming data is not limited thereto. For example, the timing data mayalternatively include an absolute time at which the connection failureoccurred (e.g., a time and date at which the connection failureoccurred). As discussed below in detail, the manner in which the nodereceives the failure report can vary depending on the particularembodiment. In general, the node can receive the failure report from theUE, from another node in the same cellular communications network, orfrom another node in another cellular communications network operatingaccording to a different RAT.

After receiving the failure report, the node determines whether theassociated connection failure occurred before a last, or most-recent,MRO adjustment made by the node (step 1002). In other words, the nodedetermines when the associated connection failure occurred with respectto the most recent MRO adjustment(s) made by the node. Morespecifically, in one embodiment, the timing data included in the failurereport includes timing data that is indicative of a time at which theconnection failure occurred. The node then determines when theassociated connection failure occurred with respect to the most recentMRO adjustment(s) based on the timing data in the failure report andtiming data maintained by the node that defines a time at which the mostrecent MRO adjustment(s) was made by the node. In one preferredembodiment discussed below, the timing data in the failure report is orincludes a timer value that defines an amount of time that has expiredbetween a time at which the connection failure occurred and a time atwhich the UE reported the connection failure by transmitting the failurereport to the appropriate node, and the timing data maintained by thenode is or includes another timer value that defines an amount of timethat has expired since the most recent MRO adjustment(s) was made by thenode. In this embodiment, the node determines when the connectionfailure occurred with respect to the most recent MRO adjustment(s) madeby the node based on a comparison of the two timer values while, in someembodiments, accounting for any delay between the reporting of theconnection failure by the UE and reception of the failure report by thenode.

In another embodiment, another node (e.g., an Operations and Maintenance(OAM) node) maintains the timer value that defines the amount of timethat has expired since the most recent MRO adjustment(s) was made by thenode. In this embodiment, the node sends the timer value from thefailure report that defines the amount of time that expired between thetime at which the connection failure occurred and the time at which theUE reported the connection failure by transmitting the failure report tothe other node. The other node then compares the two timer values while,in some embodiments, accounting for any delay between the reporting ofthe connection failure by the UE and reception of the timer value in thefailure report sent by the other node. The other node then returnsinformation to the node that is indicative of when the connectionfailure occurred with respect to the most recent MRO adjustment(s) madeby the node.

If the connection failure occurred before the most recent MROadjustment(s), the node classifies the failure report as a stale failurereport (step 1004). As such, in one embodiment, the failure report isdiscarded or otherwise not considered for a next iteration of the MROprocess. In another embodiment, the failure report is considered for thenext iteration of the MRO process with reduced relevance (e.g., reducedweighting or scaling factor as compared to timely failure reports forthe next iteration of the MRO process). If the connection failureoccurred after the most recent MRO adjustment(s), the node classifiesthe failure report as a current, or timely, failure report (step 1006).As such, the failure report is considered with full weight for the nextiteration of the MRO process.

FIG. 17 is a flow chart that illustrates the operation of a UE to reporta connection failure according to one embodiment of the presentdisclosure. As illustrated, the UE detects a connection failure (step2000). The connection failure is preferably either an RLF or a HOF. Forexample, the connection failure may be an RLF due to a too late IRAT HOfrom an LTE RAN to a 2G/3G RAN. As another example, the connectionfailure may be a HOF due to a too early IRAT HO from a 2G/3G RAN to anLTE RAN or an RLF shortly after an IRAT HO from a 2G/3G RAN to an LTERAN due to a too early IRAT HO. Note, however, that these examples arenon-limiting. Other types of connection failures (i.e., HO failures foran intra-RAT HO) may be detected, and subsequently reported, by the UE.

In response to detecting the connection failure, the UE starts a timer,which is referred to herein as timer (T_(F)) (step 2002). Thereafter,the UE continues to run the timer (T_(F)) until the UE determines thatit is time to report the connection failure (step 2004). Once it is timeto report the connection failure, the UE stops the timer (T_(F)) (step2006). In this manner, the timer (T_(F)) defines an amount of time thathas expired between a time at which the connection failure occurred andtherefore detected by the UE and a time at which the connection failureis reported by the UE. Lastly, the UE sends, or transmits, a failurereport that reports the connection failure to an appropriate node wherethe failure report includes the value of the timer (T_(F)) (step 2008).The node to which the UE sends the failure report can vary depending onthe particular embodiment. As discussed below in detail, the UE can sendthe failure report to a base station in the same RAT, or same RAN, inwhich the connection failure occurred or a base station in a differentRAT, or different RAN, than the RAT, or RAN, in which the connectionfailure occurred. Notably, whether the connection failure is an RLF or aHOF, the connection failure is reported via an RLF report.

FIG. 18 is a flow chart that illustrates the operation of a node thatperforms an MRO process to receive, classify, and utilize failurereports sent by UEs according to the process of FIG. 17 according to oneembodiment of the present disclosure. As illustrated, the node starts atimer (T_(MRO)) upon making MRO adjustment(s) for a first iteration ofthe MRO process (step 3000). Thereafter, the node receives failurereports and classifies the failure reports based on the timer (T_(MRO))and the timer (T_(F)) included in the failure reports (step 3002). Notethat the failure reports can be failure reports for multiple cells,frequencies, and/or RATs. In one embodiment, each failure report isclassified based on a comparison of the timer (T_(MRO)) at the time thatthe failure report is received by the node and the timer (T_(F)) in thefailure report such that the failure report is classified as a stalefailure report if T_(F)>T_(MRO) and classified as a current, or timely,failure report if T_(F)<T_(MRO). Note, however, that in some embodimentsthere may be a delay between the time at which the failure report issent by the corresponding UE and the time at which the failure report isreceived by the node. For example, in Solution 1, Scenario 2a, thefailure report is sent by the UE to the 2G/3G RAN and then forwarded byan RNC of the 2G/3G RAN to the LTE RAN via RAN Information Message(RIM). The forwarding of the failure report has an associated delay,which may be compensated for by the node when comparing T_(F) andT_(MRO).

At some time after a triggering event for performing the MRO process hasoccurred, the node performs a next iteration of the MRO process (step3004). In one embodiment, stale failure reports are discarded such thatthe next iteration of the MRO process performed in step 3004 isperformed based on the failure reports received and classified ascurrent in step 3002 but not based on the failure reports received andclassified as stale in step 3002. In another embodiment, stale failurereports are considered but with reduced relevance such that the nextiteration of the MRO process performed in step 3004 is performed basedon the failure reports received and classified as current in step 3002as well as the failure reports received and classified as stale in step3002 but where the stale failure reports are considered with reducedrelevance compared to the current failure reports. The relevance of thestale failure reports may be reduced by, for example, applying asuitable scaling or weighting factor to the stale failure reports.

Next, the node determines whether any MRO adjustments were made duringthe iteration of the MRO process performed in step 3004 (step 3006). Ifnot, the process returns to step 3002 and continues. If one or more MROadjustments were made in step 3004, the node restarts the timer(T_(MRO)) (step 3008) and then the process returns to step 3002 andcontinues.

FIG. 19 illustrate a multiple RAT cellular communications system 20 thatenables reporting of connection failures and classification ofcorresponding failure reports according to one embodiment of the presentdisclosure. As used herein, a multiple RAT cellular communicationssystem includes multiple cellular communications networks that operateaccording to different RATs. In this embodiment, the multiple RATcellular communications system 20 includes an LTE cellularcommunications network 22 (specifically a 4G LTE cellular communicationsnetwork 22) and a UMTS cellular communications network 23, which is a 3Gnetwork. As illustrated, the LTE cellular communications network 22includes a RAN, which is referred to herein as an LTE RAN. The LTE RANincludes base stations (BSs) 24-1 and 24-2 (more generally referred toherein collectively as base stations 24 and individually as base station24) that serve corresponding cells of the LTE cellular communicationsnetwork 22. Notably, in LTE, the base stations 24 are also referred toas eNBs.

The base station 24-1 serves UEs 26-1 through 26-N₁ (more generallyreferred to herein collectively as UEs 26 and individually as UE 26)located within the cell served by the base station 24-1. Likewise, thebase station 24-2 serves UEs 28-1 through 28-N₂ (more generally referredto herein collectively as UEs 28 and individually as UE 28) locatedwithin the cell served by the base station 24-2. It should be notedthat, as used herein, a UE is any type of device configured to operatein a cellular communications network and, in the embodiment of FIG. 19,any type of device configured to operate in the multiple RAT cellularcommunications system 20. The base station 24-1 is referred to herein asa serving base station 24-1 of the UEs 26, and the base station 24-2 isreferred to herein as a serving base station 24-2 of the UEs 28.Notably, while only two base stations 24-1 and 24-2 are illustrated inFIG. 19 for clarity and ease of discussion, it will be readilyappreciated that the LTE cellular communications network 22 can includeany number of base stations 24. Further, while not illustrated, eachbase station 24 may serve one or many cells or sectors.

The LTE cellular communications network 22 also includes a core network30 that includes one or more Serving Gateways (S-GWs) and one or moreMobility Management Entities (MMEs) (not shown). The base stations 24are connected to the core network 30 via corresponding S1 connections.Similarly, in this embodiment, the base stations 24-1 and 24-2 areconnected to one another via an X2 connection.

The UMTS cellular communications network 23 includes a RAN, which isreferred to herein as a UTRAN. The UTRAN includes RNCs 32-1 and 32-2(more generally referred to herein collectively as RNCs 32 andindividually as RNC 32). The RNC 32-1 controls a number of base stations34-1 through 34-M₁ (more generally referred to herein collectively asbase stations 34 and individually as base station 34). Likewise, the RNC32-2 controls a number of base stations 36-1 through 36-M₂ (moregenerally referred to herein collectively as base stations 36 andindividually as base station 36). The base station 34-1 serves UEs 38-1through 38-N₃ (more generally referred to herein collectively as UEs 38and individually as UE 38) located within a corresponding cell of theUMTS cellular communications network 23, and the base station 34-M₁serves UEs 40-1 through 40-N₄ (more generally referred to hereincollectively as UEs 40 and individually as UE 40) located within acorresponding cell of the UMTS cellular communications network 23. Inthe same manner, the base station 36-1 serves UEs 42-1 through 42-N₅(more generally referred to herein collectively as UEs 42 andindividually as UE 42) located within a corresponding cell of the UMTScellular communications network 23, and the base station 36-M₂ servesUEs 44-1 through 44-N₆ (more generally referred to herein collectivelyas UEs 44 and individually as UE 44) located within a corresponding cellof the UMTS cellular communications network 23. Notably, while only twoRNCs 32 are illustrated in FIG. 19 for clarity and ease of discussion,it will be readily appreciated that the UMTS cellular communicationsnetwork 23 can include any number of RNCs 32 and associated basestations. The UMTS cellular communications network 23 also includes acore network 46. The RNCs 32 are connected to the core network 46 viacorresponding connections.

The multiple RAT cellular communications system 20 includes multiple MROfunctions 48-1 through 48-4 (more generally referred to hereincollectively as MRO functions 48 and individually as MRO function 48)that operate to optimize mobility parameters for the UEs 26, 28, 38, 40,42, 44. In the LTE cellular communications network 22, the MRO functions48-1 and 48-2 are implemented at, in this example, the base stations24-1 and 24-2. Conversely, in the UMTS cellular communications network23, the MRO functions 48-3 and 48-4 are implemented at the RNCs 32-1 and32-2. In this embodiment, the MRO function 48-1 performs an MROalgorithm to adjust, or update, one or more mobility parameters thatcontrol HOs from the cell(s) served by the base station 24-1. Thesemobility parameters can be associated with RSRP and/or RSRQ measurementtypes and operate to form a HO threshold for the cell(s) served by thebase station 24-1, which is referred to herein as ho_thresh_lte. In thesame manner, the MRO function 48-2 performs an MRO algorithm to adjust,or update, one or more mobility parameters that control HOs from thecell(s) served by the base station 24-2. The MRO function 48-3 performsan MRO algorithm to adjust, or update, one or more mobility parametersthat control HOs from the cells served by the base stations 34controlled by the RNC 32-1. These mobility parameters can be associatedwith RSRP and/or RSRQ measurement types and operate to form a HOthreshold for the cell(s) served by the base station(s) 34, which isreferred to herein as ho_thresh_utran. In the same manner, the MROfunction 48-4 performs an MRO algorithm to adjust, or update, one ormore mobility parameters that control HOs from the cells served by thebase stations 36 controlled by the RNC 32-2.

As discussed below in detail, the MRO functions 48 classify failurereports associated with connection failures experienced by the UEs 26,28, 38, 40, 42, and 44 as either stale or current for a particulariteration of the MRO algorithms performed by the MRO functions 48. Inone embodiment, each failure report includes timing data that isindicative of a time at which the corresponding connection failuresoccurred. Once the failure report is received by the appropriate MROfunction 48, the MRO function 48 then classifies the failure report aseither current or stale based on the timing data as discussed above withrespect to FIGS. 16-18. If the failure report is stale, then the MROfunction 48 either discards the failure report or considers the failurereport with reduced relevance for the next iteration of the MRO process,depending on the particular embodiment.

FIGS. 20-29 illustrate the operation of the multiple RAT cellularcommunications system 20 of FIG. 19 according to several embodiments ofthe present disclosure. In particular, FIGS. 20-29 illustrate theoperation of the multiple RAT cellular communications system 20 of FIG.19 for Solutions 1-4 and Scenarios 1, 2a, and 2b. In particular, FIG. 20illustrates the operation of the multiple RAT cellular communicationssystem 20 of FIG. 19 for Solution 1, Scenario 1 according to oneembodiment of the present disclosure. As illustrated, at a time (t0),the MRO function 48 of the base station 24 (eNB) in the LTE RAN performsan iteration of the MRO process that results in one or more MROadjustments (i.e., adjustments to one or more mobility parameters). As aresult of making the MRO adjustments, the base station 24 (eNB) starts atimer (T_(MRO)). Sometime thereafter, at a time (t1), two UEs (UE1 andUE2) in the cell served by the base station 24 (eNB) experience RLFs. Inthis embodiment, the RLFs are due to too late HOs from the cell servedby the base station 24 (eNB) to a cell served by one of the basestations 34, 36 in the UTRAN. The RLFs are detected by the UEs (UE1 andUE2) and, in response, the UEs (UE1 and UE2) start corresponding timers(T_(F)).

Initially, the UEs (UE1 and UE2) reconnect to the UTRAN after the RLFs.Thereafter, at a time (t2), UE1 reconnects to the LTE RAN (e.g., by anIRAT HO from the UTRAN to the LTE RAN) and a triggering event forsending an RLF report for the RLF at t0 occurs. UE1 may reconnect to thesame cell in the LTE RAN in which the RLF occurred or a different cellin the LTE RAN. In response to the triggering event for sending the RLFreport, UE1 stops the timer (T_(F)) and transmits a failure report(i.e., an RLF report) including the value of the timer (T_(F)) to theserving base station 24 of UE1 in the LTE RAN. If the serving basestation 24 is different than the base station 24 (eNB) serving the cellin which the RLF occurred, then the serving base station 24 forwards thefailure report to the base station 24 (eNB) serving the cell in whichthe connection failure occurred. Upon receiving the failure report, theMRO function 48 of the base station 24 (eNB) classifies the failurereport based on the value of the timer (T_(F)) included in the failurereport, which in this case is t2-t1, and the value of the timer(T_(MRO)) at the base station 24 (eNB) at the time of receiving thefailure report, which in this case is t2-t0. Here, the value of thetimer (T_(F)) is less than the value of the timer (T_(MRO)) and, assuch, the failure report is classified as being current, or on time, fora next iteration of the MRO process performed by the MRO function 48 ofthe base station 24 (eNB) at a time (t3). Note that the timer (T_(MRO))is restarted at the time (t3) in response to one or more mobilityadjustments made by the MRO function 48 at the time (t3).

Sometime thereafter, at a time (t4), UE2 reconnects to the LTE RAN(e.g., by an IRAT HO from the UTRAN to the LTE RAN). UE2 may reconnectto the same cell in the LTE RAN in which the RLF occurred or a differentcell in the LTE RAN. After reconnecting to the LTE RAN, a triggeringevent for reporting the RLF failure that occurred at t0 occurs at a time(t4). The triggering event may be, for example, reception of a requestfor any failure reports from the LTE RAN. In response, UE2 stops thetimer (T_(F)) and transmits a failure report (i.e., an RLF report)including the value of the timer (T_(F)) to the serving base station 24of UE2 in the LTE RAN. If the serving base station 24 is different thanthe base station 24 (eNB) serving the cell in which the RLF occurred,then the serving base station 24 forwards the failure report to the basestation 24 (eNB) serving the cell in which the connection failureoccurred. Upon receiving the failure report, the MRO function 48 of thebase station 24 (eNB) classifies the failure report based on the valueof the timer (T_(F)) included in the failure report, which in this caseis t4-t1, and the value of the timer (T_(MRO)) at the base station 24(eNB) at the time of receiving the failure report, which in this case ist4-t3. Here, the value of the timer (T_(F)) is greater than the value ofthe timer (T_(MRO)) and, as such, the failure report is classified asbeing stale. As such, the failure report is not considered or consideredwith reduced relevance for a next iteration of the MRO process performedby the MRO function 48 of the base station 24 (eNB).

FIG. 21 illustrates the operation of the multiple RAT cellularcommunications system 20 of FIG. 19 for Solution 1, Scenario 2aaccording to one embodiment of the present disclosure. As illustrated,at a time (t0), the MRO function 48 of one of the RNCs 32 in the UTRANperforms an iteration of the MRO process that results in one or more MROadjustments (i.e., adjustments to one or more mobility parameters). As aresult of making the MRO adjustments, the RNC 32 starts a timer(T_(MRO)). Sometime thereafter, at a time (t1), two UEs (UE1 and UE2) inthe cell served by one of the base stations 34, 36 controlled by the RNC32 in the UTRAN experience HOFs during IRAT HOs from the cell served bythe base station 34, 36 to the cell served by one of the base stations24 (eNB) in the LTE RAN. In this embodiment, the HOFs are due to tooearly HOs. The HOFs are detected by the UEs (UE1 and UE2) and, inresponse, the UEs (UE1 and UE2) start corresponding timers (T_(F)).

Initially, the UEs (UE1 and UE2) reconnect to the UTRAN after the HOFs.Thereafter, at a time (t2), UE1 reconnects to the LTE RAN (e.g., by anIRAT HO from the UTRAN to the LTE RAN) and a triggering event forsending a failure report for the HOF occurs. In response to thetriggering event for sending a failure report, UE1 stops the timer(T_(F)) and transmits a failure report for the HOF including the valueof the timer (T_(F)) to the serving base station 24 of UE1 in the LTERAN. The serving base station 24 determines that the failure report isfor a HOF for an IRAT HO from the cell served by the base station 34, 36controlled by the RNC 32 and therefore forwards the failure report tothe RNC 32 via a RIM. Upon receiving the failure report, the MROfunction 48 of the RNC 32 classifies the failure report based on thevalue of the timer (T_(F)) included in the failure report, which in thiscase is t2-t1, and the value of the timer (T_(MRO)) at the RNC 32 at thetime of receiving the failure report, which in this case is t3-t0. Here,the value of the timer (T_(F)) is less than the value of the timer(T_(MRO)) and, as such, the failure report is classified as beingcurrent, or on time, for a next iteration of the MRO process performedby the MRO function 48 of the RNC 32 at a time (t4). Notably, the MROfunction 48 of the RNC 32 may compensate for a delay resulting from theforwarding of the failure report (i.e., the delay t3-t2). The timer(T_(MRO)) at the RNC 32 is restarted at the time (t4) in response to oneor more mobility adjustments made by the MRO function 48 at the time(t4).

Sometime thereafter, at a time (t5), UE2 reconnects to the LTE RAN(e.g., by an IRAT HO from the UTRAN to the LTE RAN) and a triggeringevent for sending a failure report for the HOF occurs. In response tothe triggering event for sending a failure report, UE2 stops the timer(T_(F)) and transmits a failure report for the HOF including the valueof the timer (T_(F)) to the serving base station 24 of UE2 in the LTERAN. The serving base station 24 determines that the failure report isfor a HOF for an IRAT HO from the cell served by the base station 34, 36controlled by the RNC 32 and therefore forwards the failure report tothe RNC 32 via a RIM. Upon receiving the failure report, the MROfunction 48 of the RNC 32 classifies the failure report based on thevalue of the timer (T_(F)) included in the failure report, which in thiscase is t5-t1, and the value of the timer (T_(MRO)) at the RNC 32 at thetime of receiving the failure report, which in this case is t6-t4. Here,the value of the timer (T_(F)) is greater than the value of the timer(T_(MRO)) and, as such, the failure report is classified as being stalefor a next iteration of the MRO process performed by the MRO function 48of the RNC 32. Notably, the MRO function 48 of the RNC 32 may compensatefor a delay resulting from the forwarding of the failure report (i.e.,the delay t6-t5). The timer (T_(MRO)) at the RNC 32 is restarted at thetime (t4) in response to one or more mobility adjustments made by theMRO function 48 at the time (t4). Since the failure report from UE2 isstale, the failure report is not considered or is considered withreduced relevance for the next iteration of the MRO process performed bythe MRO function 48 of the RNC 32. It should also be noted that the MROfunction 48 of the cell in the LTE RAN may also receive and utilize thefailure report, if desired.

FIG. 22 illustrates the operation of the multiple RAT cellularcommunications system 20 of FIG. 19 for Solution 1, Scenario 2baccording to one embodiment of the present disclosure. This embodimentis the same as that of FIG. 21 but where the connection failure is anRLF failure shortly after a successful IRAT HO. As such, the details arenot repeated.

FIG. 23 illustrates the operation of the multiple RAT cellularcommunications system 20 of FIG. 19 for Solution 2, Scenario 1 accordingto one embodiment of the present disclosure. As illustrated, at a time(t0), the MRO function 48 of one of the base stations 24 (eNB) in theLTE RAN performs an iteration of the MRO process that results in one ormore MRO adjustments (i.e., adjustments to one or more mobilityparameters). As a result of making the MRO adjustments, the base station24 (eNB) starts a timer (T_(MRO)). Sometime thereafter, at a time (t1),two UEs (UE1 and UE2) in the cell served by the base station 24 (eNB)experience RLFs. In this embodiment, the RLFs are due to too late HOsfrom the cell served by the base station 24 (eNB) to a cell served byone of the base stations 34, 36 in the UTRAN. The RLFs are detected bythe UEs (UE1 and UE2) and, in response, the UEs (UE1 and UE2) startcorresponding timers (T_(F)).

Sometime thereafter, at a time (t2), UE1 reconnects to the cell of oneof the base stations 34, 36 of one of the RNCs 32 in the UTRAN and atriggering event for sending an RLF report for the RLF at t0 occurs. Inresponse to the triggering event for sending the RLF report, UE1 stopsthe timer (T_(F)) and transmits a failure report (i.e., an RLF report)including the value of the timer (T_(F)) to the serving base station 34,36 of UE1 in the UTRAN, which in turn communicates the RLF report to theRNC 32. The RNC 32 determines that the RLF report is associated with anRLF that occurred in the cell served by the base station 24 (eNB) in theLTE RAN and therefore forwards the RLF report to the base station 24(eNB) via a RIM at a time (t3).

Upon receiving the failure report, the MRO function 48 of the basestation 24 (eNB) classifies the failure report based on the value of thetimer (T_(F)) included in the failure report, which in this case ist2-t1, and the value of the timer (T_(MRO)) at the base station 24 (eNB)at the time of receiving the failure report, which in this case ist3-t0. Here, the value of the timer (T_(F)) is less than the value ofthe timer (T_(MRO)) and, as such, the failure report is classified asbeing current, or on time, for a next iteration of the MRO processperformed by the MRO function 48 of the base station 24 (eNB) at a time(t4). Note that the MRO function 48 may compensate for a delayassociated with forwarding the RLF report from the RNC 32 to the basestation 24 (eNB), which in this example is t3-t2. The timer (T_(MRO)) isrestarted at the time (t3) in response to one or more mobilityadjustments made by the MRO function 48 at the time (t4).

Sometime thereafter, at a time (t5), UE2 reconnects to the cell of oneof the base stations 34, 36 of one of the RNCs 32 in the UTRAN and atriggering event for sending an RLF report for the RLF at t0 occurs. Inresponse to the triggering event for sending the RLF report, UE2 stopsthe timer (T_(F)) and transmits a failure report (i.e., an RLF report)including the value of the timer (T_(F)) to the serving base station 34,36 of UE2 in the UTRAN, which in turn communicates the RLF report to theRNC 32. The RNC 32 determines that the RLF report is associated with anRLF that occurred in the cell served by the base station 24 (eNB) in theLTE RAN and therefore forwards the RLF report to the base station 24(eNB) via a RIM at a time (t6). Upon receiving the failure report, theMRO function 48 of the base station 24 (eNB) classifies the failurereport based on the value of the timer (T_(F)) included in the failurereport, which in this case is t5-t1, and the value of the timer(T_(MRO)) at the base station 24 (eNB) at the time of receiving thefailure report, which in this case is t6-t4. Here, the value of thetimer (T_(F)) is greater than the value of the timer (T_(MRO)) and, assuch, the failure report is classified as being stale for a nextiteration of the MRO process performed by the MRO function 48 of thebase station 24 (eNB). Note that the MRO function 48 may compensate fora delay associated with forwarding the RLF report from the RNC 32 to thebase station 24 (eNB), which in this example is t6-t5. Since the failurereport from UE2 is stale, the failure report is not considered or isconsidered with reduced relevance for the next iteration of the MROprocess performed by the MRO function 48 of the base station 24 (eNB).

FIG. 24 illustrates the operation of the multiple RAT cellularcommunications system 20 of FIG. 19 for Solution 2, Scenario 2aaccording to one embodiment of the present disclosure. As illustrated,at a time (t0), the MRO function 48 of one of the base stations 24 (eNB)in the LTE RAN performs an iteration of the MRO process that results inone or more MRO adjustments (i.e., adjustments to one or more mobilityparameters). As a result of making the MRO adjustments, the base station24 (eNB) starts a timer (T_(MRO)). In addition, at a time (t0′), the MROfunction 48 of one of the RNCs 32 in the UTRAN performs an iteration ofthe MRO process that results in one or more MRO adjustments (i.e.,adjustments to one or more mobility parameters). As a result of makingthe MRO adjustments, the RNC 32 starts a timer (T_(MRO)). Sometimethereafter, at a time (t1), two UEs (UE1 and UE2) in the cell served byone of the base stations 34, 36 controlled by the RNC 32 in the UTRANexperience HOFs during IRAT HOs from the cell served by the base station34, 36 to the cell served by one of the base stations 24 (eNB) in theLTE RAN. In this embodiment, the HOFs are due to too early HOs. The HOFsare detected by the UEs (UE1 and UE2) and, in response, the UEs (UE1 andUE2) start corresponding timers (T_(F)).

Thereafter, at a time (t2), UE1 reconnects to one of the cells in theUTRAN and a triggering event for sending a failure report for the HOFoccurs. UE1 may reconnect to the same cell in which the HOF occurred ora different cell. In response to the triggering event for sending afailure report, UE1 stops the timer (T_(F)) and transmits a failurereport for the HOF including the value of the timer (T_(F)) to theserving base station 34, 36 of UE1 in the UTRAN. The serving basestation 34, 36 determines that the failure report is for a HOF for anIRAT HO from the cell served by the base station 34, 36 controlled bythe RNC 32 to the cell served by one of the base stations 24 (eNB) inthe LTE RAN. If the RNC 32 of the serving base station 34, 36 isdifferent than the RNC 32 of the base station 34, 36 serving the cell inwhich the HOF occurred, the RNC 32 forwards the failure report to theRNC 32 of the base station 34, 36 serving the cell in which the HOFoccurred. In addition, in this example, the RNC 32 forwards the failurereport to the base station 24 (eNB) in the LTE RAN that was the targetof the failed IRAT HO via a RIM.

Upon receiving the failure report, the base station 24 (eNB) in the LTERAN classifies the failure report based on the value of the timer(T_(F)) included in the failure report, which in this case is t2-t1, andthe value of the timer (T_(MRO)) at the base station 24 (eNB) at thetime of receiving the failure report, which in this case is t3-t0. Here,the value of the timer (T_(F)) is less than (T_(MRO)) and, as such, thefailure report is classified as being current, or on time, for a nextiteration of the MRO process performed by the MRO function 48 of thebase station 24 (eNB) at a time (t4). Notably, the MRO function 48 ofthe base station 24 (eNB) may compensate for a delay resulting from theforwarding of the failure report (i.e., the delay t3-t2). The timer(T_(MRO)) at the base station 24 (eNB) is restarted at the time (t4) inresponse to one or more mobility adjustments made by the MRO function 48at the time (t4).

At the RNC 32, the MRO function 48 of the RNC 32 classifies the failurereport based on the value of the timer (T_(F)) included in the failurereport, which in this case is t2-t1, and the value of the timer(T_(MRO)) at the RNC 32 at the time of receiving the failure report,which in this case is t2-t0′. Here, the value of the timer (T_(F)) isless than (T_(MRO)) and, as such, the failure report is classified asbeing current, or on time, for a next iteration of the MRO processperformed by the MRO function 48 of the RNC 32 at a time (t3′). Thetimer (T_(MRO)) at the RNC 32 is restarted at the time (t3′) in responseto one or more mobility adjustments made by the MRO function 48 at thetime (t3′).

Sometime thereafter, at a time (t5), UE2 reconnects to one of the cellsin the UTRAN and a triggering event for sending a failure report for theHOF occurs. UE2 may reconnect to the same cell in which the HOF occurredor a different cell. In response to the triggering event for sending afailure report, UE2 stops the timer (T_(F)) and transmits a failurereport for the HOF including the value of the timer (T_(F)) to theserving base station 34, 36 of UE2 in the UTRAN. The serving basestation 34, 36 determines that the failure report is for a HOF for anIRAT HO from the cell served by the base station 34, 36 controlled bythe RNC 32 to the cell served by one of the base stations 24 (eNB) inthe LTE RAN. If the RNC 32 of the serving base station 34, 36 isdifferent than the RNC 32 of the base station 34, 36 serving the cell inwhich the HOF occurred, the RNC 32 forwards the failure report to theRNC 32 of the base station 34, 36 serving the cell in which the HOFoccurred. In addition, in this example, the RNC 32 forwards the failurereport to the base station 24 (eNB) in the LTE RAN that was the targetof the failed IRAT HO via a RIM.

Upon receiving the failure report, the base station 24 (eNB) in the LTERAN classifies the failure report based on the value of the timer(T_(F)) included in the failure report, which in this case is t5-t1, andthe value of the timer (T_(MRO)) at the base station 24 (eNB) at thetime of receiving the failure report, which in this case is t6-t4. Here,the value of the timer (T_(F)) is greater than (T_(MRO)) and, as such,the failure report is classified as being stale for a next iteration ofthe MRO process performed by the MRO function 48 of the base station 24(eNB). Notably, the MRO function 48 of the base station 24 (eNB) maycompensate for a delay resulting from the forwarding of the failurereport. Since the failure report from UE2 is stale, the failure reportis not considered or is considered with reduced relevance for the nextiteration of the MRO process performed by the MRO function 48 of thebase station 24 (eNB).

At the RNC 32, the MRO function 48 of the RNC 32 classifies the failurereport from UE2 based on the value of the timer (T_(F)) included in thefailure report, which in this case is t5-t1, and the value of the timer(T_(MRO)) at the RNC 32 at the time of receiving the failure report,which in this case is t5-t3′. Here, the value of the timer (T_(F)) isgreater than (T_(MRO)) and, as such, the failure report is classified asbeing stale for a next iteration of the MRO process performed by the MROfunction 48 of the RNC 32. Since the failure report from UE2 is stale,the failure report is not considered or is considered with reducedrelevance for the next iteration of the MRO process performed by the MROfunction 48 of the RNC 32.

FIG. 25 illustrates the operation of the multiple RAT cellularcommunications system 20 of FIG. 19 for Solution 2, Scenario 2baccording to one embodiment of the present disclosure. This embodimentis the same as that of FIG. 24 but where the connection failure is anRLF failure shortly after a successful IRAT HO. As such, the details arenot repeated.

FIGS. 26-28 illustrate the operation of the multiple RAT cellularcommunications system 20 of FIG. 21 for Solution 3, Scenarios 1, 2a, and2b, respectively. For Solution 3, an RLF is reported in the RAT wherethe connection failure occurred and a HOF is reported in the RAT of thecell in which the HO command was received. Solution 3 for Scenarios 1,2a, and 2b are therefore the same as Solution 1, Scenario 1, Solution 2,Scenario 2a, and Solution 1, Scenario 2b, respectively. The operation ofthe multiple RAT cellular communications system 20 for these embodimentsis the same as that discussed above with respect to FIG. 20 (Solution 1,Scenario 1), FIG. 24 (Solution 2, Scenario 2a), and FIG. 22 (Solution 1,Scenario 2b), respectively. As such, the details are not repeated.

FIG. 29 illustrates the operation of the multiple RAT cellularcommunications system 20 of FIG. 19 for Solution 4, Scenario 1. Theoperation of the multiple RAT cellular communications system 20 for thisembodiment is the same as that discussed above with respect to FIG. 20(Solution 1, Scenario 1). As such, the details are not repeated. ForSolution 4, Scenarios 2a and 2b, the connection failure is not reportedby the UE, but is rather detected by the appropriate RNC 32. Note thatwhile FIGS. 20-29 focus on IRAT HOs, the systems and methods disclosedherein are equally applicable to reporting of other types of mobilityconnection failures such as, for example, connection failures forintra-RAT HOs.

FIG. 30 is a block diagram of a UE 50 according to one embodiment of thepresent disclosure. This discussion of the UE 50 is equally applicableto the UEs 26, 28, 38, 40, 42, and 44 of FIG. 19. As illustrated, the UE50 includes a radio subsystem 52 and a processing subsystem 54. Theradio subsystem 52 includes one or more transceivers (not shown)generally including analog and, in some embodiments, digital componentsfor sending and receiving data to and from the cellular communicationsnetworks 22 and 23 (FIG. 19). In particular embodiments, each of the oneor more transceivers may represent or include one or more RadioFrequency (RF) transceivers, or separate RF transmitter(s) andreceiver(s), capable of transmitting suitable information wirelessly toand receiving suitable information from other network components ornodes. From a wireless communications protocol view, the radio subsystem52 implements at least part of Layer 1 (i.e., the Physical or “PHY”Layer).

The processing subsystem 54 generally implements any remaining portionof Layer 1 as well as functions for higher layers in the wirelesscommunications protocol (e.g., Layer 2 (data link layer), Layer 3(network layer), etc.). In particular embodiments, the processingsubsystem 54 may comprise, for example, one or several general-purposeor special-purpose microprocessors or other microcontrollers programmedwith suitable software and/or firmware to carry out some or all of thefunctionality of the UE 50 described herein. In addition oralternatively, the processing subsystem 54 may comprise various digitalhardware blocks (e.g., one or more Application Specific IntegratedCircuits (ASICs), one or more off-the-shelf digital and analog hardwarecomponents, or a combination thereof) configured to carry out some orall of the functionality of the UE 50 described herein. Additionally, inparticular embodiments, the above-described functionality of the UE 50may be implemented, in whole or in part, by the processing subsystem 54executing software or other instructions stored on a non-transitorycomputer-readable medium, such as Random Access Memory (RAM), Read OnlyMemory (ROM), a magnetic storage device, an optical storage device, orany other suitable type of data storage components. Of course, thedetailed operation for each of the functional protocol layers, and thusthe radio subsystem 52 and the processing subsystem 54, will varydepending on both the particular implementation as well as the standardor standards supported by the UE 50.

FIG. 31 is a block diagram of a base station 56 according to oneembodiment of the present disclosure. This discussion of the basestation 56 is equally applicable to the base stations 24, 34, and 36 ofFIG. 19. As illustrated, the base station 56 includes a radio subsystem58, one or more communication interfaces 60, and a processing subsystem62. While only one radio subsystem 58 is illustrated, the base station56 may include multiple radio subsystems 58 (e.g., one radio subsystem58 per sector). The radio subsystem 58 generally includes analog and, insome embodiments, digital components for sending and receiving data toand from UEs within the corresponding cell. In particular embodiments,the radio subsystem 58 may represent or include one or more RFtransceiver(s), or separate RF transmitter(s) and receiver(s), capableof transmitting suitable information wirelessly to and receivingsuitable information from other network components or nodes. From awireless communications protocol view, the radio subsystem 58 implementsat least part of Layer 1 (i.e., the Physical or “PHY” Layer).

The one or more communication interfaces 60 provide connectivity toother network nodes as appropriate. For instance, the one or morecommunication interfaces 60 may include communication interface(s) toother base stations 56 (e.g., an X2 interface in the LTE cellularcommunications network 22) and communication interface(s) to thecorresponding core network 30, 46 (e.g., S1 communication interface inthe LTE cellular communications network 22).

The processing subsystem 62 generally implements any remaining portionof Layer 1 not implemented in the radio subsystem 58 as well asfunctions for higher layers in the wireless communications protocol(e.g., Layer 2 (data link layer), Layer 3 (network layer), etc.). Inparticular embodiments, the processing subsystem 62 may comprise, forexample, one or several general-purpose or special-purposemicroprocessors or other microcontrollers programmed with suitablesoftware and/or firmware to carry out some or all of the functionalityof the base station 56 described herein. In addition or alternatively,the processing subsystem 62 may comprise various digital hardware blocks(e.g., one or more ASICs, one or more off-the-shelf digital and analoghardware components, or a combination thereof) configured to carry outsome or all of the functionality of the base station 56 describedherein. Additionally, in particular embodiments, the above describedfunctionality of the base station 56 may be implemented, in whole or inpart, by the processing subsystem 62 executing software or otherinstructions stored on a non-transitory computer-readable medium, suchas RAM, ROM, a magnetic storage device, an optical storage device, orany other suitable type of data storage components.

Lastly, FIG. 32 is a block diagram of one of the RNCs 32 of FIG. 19according to one embodiment of the present disclosure. As illustrated,the RNC 32 includes one or more communication interfaces 64 and aprocessing subsystem 66. The one or more communication interfaces 64provide connectivity to other network nodes as appropriate. Inparticular, the one or more communication interfaces 64 includecommunication interface(s) to the corresponding base stations 34, 36(FIG. 19) and communication interface(s) to the core network 46. Theprocessing subsystem 66 may comprise, for example, one or severalgeneral-purpose or special-purpose microprocessors or othermicrocontrollers programmed with suitable software and/or firmware tocarry out some or all of the functionality of the RNC 32 describedherein. In addition or alternatively, the processing subsystem 66 maycomprise various digital hardware blocks (e.g., one or more ASICs, oneor more off-the-shelf digital and analog hardware components, or acombination thereof) configured to carry out some or all of thefunctionality of the RNC 32 described herein. Additionally, inparticular embodiments, the above described functionality of the RNC 32may be implemented, in whole or in part, by the processing subsystem 66executing software or other instructions stored on a non-transitorycomputer-readable medium, such as RAM, ROM, a magnetic storage device,an optical storage device, or any other suitable type of data storagecomponents.

As discussed above, conventional connection failure reporting results indelays between the time at which connection failures occur and the timeat which the connection failures are reported to the network. Delays inreporting the connection failure may be due to a long delay before theUE reconnects to the RAN where the connection failure is to be reported(e.g., Solution 1), due to the UE transitioning to an idle mode for along time before reconnecting to the RAN where the connection failure isto be reported, or due to a failure of the cellular communicationsnetwork to request reporting of the RLF report for a long time. Thus, anMRO function that performs MRO for a cell in, for example, an LTE RANmay perform an MRO process that results in adjustment(s) to mobilityparameters (i.e., mobility adjustments) for the cell based on failurereports received in a timely manner. However, due to the issue ofdelayed reporting, the MRO function may continue to receive failurereports after the mobility adjustment(s) have been made where thefailure reports are relevant to a time window prior to making themobility adjustment(s). Using conventional MRO algorithms, these “stale”failure reports are still considered with the same relevance as timelyfailure reports for the next iteration of the MRO process. The stalefailure reports may lead to incorrect or undesirable mobilityadjustments and slow convergence of the cellular communications networkto a state of stable mobility.

While the concepts disclosed herein are not limited to any particularadvantage, the concepts disclosed herein address the issue of delayedconnection failure reporting. In particular, using appropriate timingdata, failure reports are classified as stale or current. Stale failurereports can then be discarded or used in a subsequent iteration of theMRO algorithm. As a result, incorrect or undesirable mobilityadjustments and slow convergence of the cellular communications networkto a state of stable mobility due to delayed failure reports areavoided.

The following acronyms are used throughout this disclosure.

-   -   3GPP 3^(rd) Generation Partnership Project    -   ASIC Application Specific Integrated Circuit    -   BS Base Station    -   EDGE Enhanced Data Rates for Global Evolution    -   eNB Enhanced Node B    -   GERAN Global System for Mobile Communications Enhanced Data        Rates for Global Evolution Radio Access Network    -   GSM Global System for Mobile Communications    -   HO Handover    -   HOF Handover Failure    -   IRAT Inter-Radio Access Technology    -   LTE Long Term Evolution    -   MME Mobility Management Entity    -   MRO Mobility Robustness Optimization    -   OAM Operations and Maintenance    -   RACH Random Access Channel    -   RAM Random Access Memory    -   RAN Radio Access Network    -   RAT Radio Access Technology    -   RF Radio Frequency    -   RIM Radio Access Network Information Message    -   RLF Radio Link Failure    -   RNC Radio Network Controller    -   RRC Radio Resource Control    -   RSRP Reference Signal Received Power    -   RSRQ Reference Signal Received Quality    -   S-GW Serving Gateway    -   TS Technical Specification    -   UE User Equipment or User Element    -   UMTS Universal Mobile Telecommunications System    -   UTRAN Universal Terrestrial Radio Access Network    -   WG3 Working Group 3

Those skilled in the art will recognize improvements and modificationsto the preferred embodiments of the present disclosure. All suchimprovements and modifications are considered within the scope of theconcepts disclosed herein and the claims that follow.

What is claimed is:
 1. A method of operation of a user equipment,comprising: detecting a connection failure in a cellular communicationsnetwork; starting a timer in response to detecting the connectionfailure; detecting a triggering event for transmitting a failure reportassociated with the connection failure; and in response to thetriggering event: stopping the timer; and transmitting a failure report,the failure report being associated with the connection failure andincluding a timer value that defines an amount of time between the timeat which the connection failure occurred and a time at which the userequipment transmits the failure report.
 2. The method of claim 1 whereinthe connection failure is a radio link failure in a cell served by afirst base station in a first radio access network operating accordingto a first radio access technology, and the method further comprises:initially reconnecting to a base station in a second radio accessnetwork operating according to a second radio access technology afterthe radio link failure; and subsequently connecting to a base station inthe first radio access network to thereby reconnect to the first radioaccess network; wherein transmitting the failure report comprisestransmitting the failure report to the base station in the first radioaccess network after reconnecting to the first radio access network. 3.The method of claim 2 wherein the base station to which the failurereport is transmitted is one of the group consisting of: the first basestation in the first radio access network and a second base station inthe first radio access network that is different than the first basestation.
 4. The method of claim 1 wherein the connection failure is aconnection failure associated with a handover from a cell served by afirst base station in a first radio access network operating accordingto a first radio access technology to a cell served by a second basestation in a second radio access network operating according to a secondradio access technology, and the method further comprises: initiallyconnecting to a base station in the first radio access network after theconnection failure; and subsequently connecting to a base station in thesecond radio access network; wherein transmitting the failure reportcomprises transmitting the failure report to the base station in thesecond radio access network after connecting to the base station in thesecond radio access network.
 5. The method of claim 4 wherein theconnection failure is a handover failure.
 6. The method of claim 4wherein the connection failure is a radio link failure just aftercompleting the handover from the cell served by the first base stationin the first radio access network to the cell served by the second basestation in the second radio access network.
 7. The method of claim 1wherein the connection failure is a radio link failure in a cell servedby a first base station in a first radio access network operatingaccording to a first radio access technology, and the method furthercomprises: connecting to a second base station in a second radio accessnetwork operating according to a second radio access technology afterthe radio link failure; wherein transmitting the failure reportcomprises transmitting the failure report to the second base station inthe second radio access network after connecting to the second basestation of the second radio access network.
 8. The method of claim 1wherein the connection failure is a connection failure associated with ahandover from a cell served by a first base station in a first radioaccess network operating according to a first radio access technology toa cell served by a second base station in a second radio access networkoperating according to a second radio access technology, and the methodfurther comprises: initially connecting to a base station in the firstradio access network after the connection failure; wherein transmittingthe failure report comprises transmitting the failure report to the basestation in the first radio access network after connecting to the basestation in the first radio access network.
 9. The method of claim 8wherein the connection failure is a handover failure.
 10. The method ofclaim 8 wherein the connection failure is a radio link failure justafter completing the handover from the cell served by the first basestation in the first radio access network to the cell served by thesecond base station in the second radio access network.
 11. The methodof claim 1 wherein the connection failure is a connection failureassociated with a handover from a first cell served by a first basestation in a radio access network operating according to a radio accesstechnology to a second cell served by a second base station in the radioaccess network.
 12. A user equipment, comprising: a radio subsystem; anda processing subsystem associated with the radio subsystem configuredto: detect a connection failure in a cellular communications networkstart a timer in response to detecting the connection failure; detect atriggering event for transmitting a failure report associated with theconnection failure; and in response to the triggering event: stop thetimer; and transmit a failure report via the radio subsystem, thefailure report being associated with the connection failure andincluding a timer value that defines an amount of time that has expiredbetween a time at which the connection failure occurred and a time atwhich the user equipment transmitted the failure report.
 13. The userequipment of claim 12 wherein the connection failure is a radio linkfailure in a cell served by a first base station in a first radio accessnetwork operating according to a first radio access technology, and theprocessing system is further configured to: initially reconnect to abase station in a second radio access network operating according to asecond radio access technology after the radio link failure; andsubsequently connect to a base station in the first radio access networkto thereby reconnect to the first radio access network; whereintransmitting the failure report comprises transmit the failure report tothe base station in the first radio access network after reconnecting tothe first radio access network.
 14. The user equipment of claim 13wherein the base station to which the failure report is transmitted isone of the group consisting of: the first base station in the firstradio access network and a second base station in the first radio accessnetwork that is different than the first base station.
 15. The userequipment of claim 12 wherein the connection failure is a connectionfailure associated with a handover from a cell served by a first basestation in a first radio access network operating according to a firstradio access technology to a cell served by a second base station in asecond radio access network operating according to a second radio accesstechnology, and the processing system is further configured to:initially connect to a base station in the first radio access networkafter the connection failure; and subsequently connect to a base stationin the second radio access network; wherein transmitting the failurereport comprises transmit the failure report to the base station in thesecond radio access network after connecting to the base station in thesecond radio access network.
 16. The user equipment of claim 15 whereinthe connection failure is a radio link failure just after completing thehandover from the cell served by the first base station in the firstradio access network to the cell served by the second base station inthe second radio access network.
 17. The user equipment of claim 12wherein the connection failure is a radio link failure in a cell servedby a first base station in a first radio access network operatingaccording to a first radio access technology, and the processing systemis further configured to: connect to a second base station in a secondradio access network operating according to a second radio accesstechnology after the radio link failure; wherein transmitting thefailure report comprises transmit the failure report to the second basestation in the second radio access network after connecting to thesecond base station of the second radio access network.
 18. The userequipment of claim 12 wherein the connection failure is a connectionfailure associated with a handover from a cell served by a first basestation in a first radio access network operating according to a firstradio access technology to a cell served by a second base station in asecond radio access network operating according to a second radio accesstechnology, and the processing system is further configured to:initially connect to a base station in the first radio access networkafter the connection failure; wherein transmitting the failure reportcomprises transmit the failure report to the base station in the firstradio access network after connecting to the base station in the firstradio access network.
 19. The user equipment of claim 18 wherein theconnection failure is a radio link failure just after completing thehandover from the cell served by the first base station in the firstradio access network to the cell served by the second base station inthe second radio access network.
 20. The user equipment of claim 12wherein the connection failure is a connection failure associated with ahandover from a first cell served by a first base station in a radioaccess network operating according to a radio access technology to asecond cell served by a second base station in the radio access network.